Extreme pressure,rust preventive synthetic base grease

ABSTRACT

GREASE LUBRICANTS FOR MILITARY AND INDUSTRIAL USE CONSISTING OF ABOUT 65 TO 75 WEIGHT PERCENT TRIMETHYLOLPROPANE ESTER OF STRAIGHT CHAIN MONOCARBOXYLIC ACIDS HAVING 5 TO 7 CARBON ATOMS, 25 TO 35 WEIGHT PERCENT POLYTETRAFLUOROETHYLENE HAVING A MOLECULAR WEIGHT 10,000 TO 50,000 AND 0.25 TO 0.75 WEIGHT PERCENT SODIUM NITRITE, THE GREASE EXHIBITING EXCELLENT EXTREME PRESSURE PROPERTIES AS WELL AS RUST PREVENTION CHARACTERISTICS.

United States Patent Ofice 3,689,411 EXTREME PRESSURE, RUST PREVENTIVE SYNTHETIC BASE GREASE Joseph F. Messina, Havertown, Henry Gisser, Philadelphia, Pa., assignors to the United States of America as represented by the Secretary of the Army No Drawing. Filed Apr. 6, 1971, Ser. No. 131,774 Int. Cl. Cm 7/24, 7/28 US. Cl. 252-45 4 Claims ABSTRACT OF THE DISCLOSURE The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to us of any royalty thereon.

Reference is hereby made to patent application Ser. No. 131,773 of Messina et al. for Extreme Pressure, Rust Preventive, Nonreactive Greases filed concurrently herewith, and patent application Ser. No. 861,487, filed Sept. 26, 1969 of Messina et al. for Grease Compositions, both assigned to the same assignee of this patent application.

This invention relates to improved lubricants and more particularly concerns synthetic base grease compositions having good extreme pressure properties.

In patent application Ser. No. 861,487 above-mentioned, it is stated that greases having desirable properties with respect to long term stability, high temperature stability, and unusually good low temperature properties are available with compositions comprising trimethylolpropane (TMP) esters thickened with polytetrafiuoroethylene (PTFE). For severe military applications, it would be desirable if the load carrying capacities and rust protection properties of these greases could be enhanced.

Accordingly, it is an object of this invention to provide such greases for severe military and industrial applications, the greases exhibiting good extreme pressure and rust protecting properties.

Other and further objects of the invention will become apparent as the invention is further hereinafter described.

Briefly, we have discovered that when minor amounts of sodium nitrite are added to TMP esters of certain fatty acids which have been thickened with a perfiuoro polymer, that improved load carrying capabilities and rust inhibition qualities of the greases result.

More specifically, we have discovered that TMP esters of n-valeric, n-hexanoic and n-heptoic acids in any proportion, or any alone, when thickened with PTFE having a molecular weight of about 10,000 to 50,000, and including about 0.25 to 0.75 weight percent NaNO- yields a grease-type lubricant having improved extreme pressure properties, thus making it ideally suitable for severe military applications.

NaNO has been used previously as a rust-inhibiting additive. However, its remarkable improvement of extreme pressure qualities of our synthetic base PTFE-grease system was totally unexpected.

Typical properties of the PTFE solids used in the preparation of our inventive compositions are:

A softening point of 321.1 C.

3,689,41 l Patented Sept. 5, 1972 A particle size under 30 microns in diameter, the PTFE solids being supplied as a 7.5% suspension in trichlorotrifluoroethane.

The viscosity of the TMP esters of the C C and C acids, approximately 6 of each, by weight, is 15.1 centistokes at 100 F. Of course, since the viscosity of the TMP ester of C acid is higher than the corresponding TMP esters of C or C acids, the viscosity will be increased as th e proportion of the TMP ester of 0; acid is increased.

The grease was prepared as follows:

The dispersion of PTFE in trichlorotrifluoroethane was heated on a steam bath until 50 to of the solvent evaporated. Approximately 75% of the required quantity of TMP ester was then added, the mixture was stirred and heating continued until all the trichlorotrifluoroethane had evaporated.

(The absence of trichlorotrifluoroethane. was determined by gas chromatography using the following technique. A sample of the grease mixture was extracted using OR benzene. The extracted fluid mixture was placed in a gas chromatograph with a 20 foot carbowax 20 M column at 50 C. and a helium gas flow of 10 ml. per minute. Absence of a retention peak after 3.3 minutes indicated that all of the trichlorotrifluoroethane had evaporated.) The remainder of the TMP fluid was then added while stirring, and stirring continued until a homogeneous grease-like product was obtained. The mixture was cooled to room temperature. Sodium nitrite was then added and thoroughly mixed into the grease by passing the grease twice through a colloid mill with stator-to-rotor clearance set at 0.001 inch. The homogenized mixture was then placed in a freezer at minus 10 C. for 24 hours, removed and permitted to remain at room temperature an addi tional 24 hours prior to use.

The viscosity of the TMP fluid increases slightly as of the ester of the n-heptoic acids are used, as compared to the ester of the n-valeric acid. All values presented in Tables I and II below were obtained on a mixture of about A by weight of each of the TMP esters of n-valeric, n-hexanoic and n-heptoic acids, balance being PTFE thickener and NaNO TABLE I.LOAD CARRYING CAPACITY Composition, wt. Weld, kg. (ASTM percent D 2596-69) 73.50%+26.50% PTFE 360 '73.50%+26.25% P='IFE+0.25% Na'NO 550 The PTFE used in Table I above and Table II below had a molecular weight between about 10,000 to 50,000 and the N'aNO used throughout was of technical grade powder, having a particle size of approximately 10 microns, or smaller. While all values in both tables were obtained using a mixture of approximately /3 by weight each of the TMP esters of C C vand C acids, comparable data were obtained using other proportions of any of these esters, singly or combined. The TMP esters may range between about 65 to 75 weight percent; the PTFE thickener may range between about 25 to 35 weight percent; and the NaNO- may range between about 0.25 to 0.75 weight percent. As shown in the table above, data were obtained in accordance with ASTM D 2596-69'.

The rust prevention properties of our grease are tabulated in Table II below, the data being obtained in accordance with ASTM D 1743-64, wherein lubricated tapered roller bearings, SAE 4620 or 8720 ferrous alloy with 1010 mild steel roller retainers, were exposed to 100% of relative humidity for 14 days at 25 10.5 C. This test is accepted for greases used by the military and is currently specified in numerous Government specifications.

The bearings lubricated with our greases showed no corrosion whereas those without the NaNO rusted badly.

TABLE IL-RUST PREVENTION Composition wt. Rust test (ASTM percent D 1743-64) 73.50% TMP+26.50% PTFE Fail 73.50% TMP+26.25% PTFE+0.25%

NaNO Pass It is apparent from the foregoing that we have provided grease compositions of synthetic base for use under the severest of military applications, the rust-preventive greases having good long term and high temperature stability with desirable low temperature properties, and yet having markedly improved load carrying capabilities.

We wish it to be understood that we do not desire to be limited to the exact details described for obvious modifications will occur to a person skilled in the art.

.We claim:

1. An extreme pressure lubricating grease composition comprising, by Weight, about 65 to 75% trimethylolpropane esters of straight chain monocarboxylic acids having 5 to 7 carbon atoms, about 25 to 35% polytetrafluoroethylene having a molecular weight 10,000 to 50,000, and about 0.25 to 0.75% sodium nitrite.

2. The composition of claim 1 wherein said esters of n-valeric, n-hexanoic and n-heptoic may be in any proportions whatsoever. 7 e

3. The composition of claim 2 wherein said esters of n-valeric, n-hexanoic and n-heptoic are present in about equal amounts.

4. The composition of claim 3 wherein said trimethylolpropane ester is present in an amount of 73.50 weight percent, said polytetrafluoroethylene is present in, an amount of 26.25 Weight percent, and said sodium nitrite is present in an amount of 0.25 weight percent.

References Cited UNITED STATES PATENTS 3,011,975 12/1961 Nitzeche et al; 25225 3,476,685 11/1969. Oberender et a1. 25256 S 3,505,229 4/1970 Skehan 25254 3,525,690 8/1970 Christian 252 -54 3,579,448 5/1971 Harrison "25256 S 3,622,512 11/1971 Christian 25256 S DANIEL E. WYMAN, Primary Examiner I. VAUGHN, Assistant Examiner us. 01. X.R. 25256 5, 387 

